The electrophilic addition of liquid bromine () to *trans*-2-butene is a stereospecific reaction. Wh — Hydrocarbons Chemistry Question

💡 Solution & Explanation

The halogenation of alkenes with $Br_2$ proceeds via a cyclic bromonium ion intermediate and involves strict *anti*-addition. The *anti*-addition of halogens to a *trans* symmetrically substituted alkene yields a *meso* compound (due to an internal plane of symmetry). Conversely, *anti*-addition to a *cis* alkene yields a racemic mixture. Thus, *meso*-2,3-dibromobutane is formed.